As the availability of potable drinking water diminishes, it is becoming more and more necessary to utilize alternate sources of water to supply the needs of a household. One readily available and easy to collect alternate source of water is rainwater. Using appropriately configured gutters, the water shed off of a roof can be directed into water storage tanks to collect many gallons of water over a short period of time. For example, 1 inch of rain over a 1000 ft2 of roof surface corresponds to over 600 gallons. On a rainy day, a light rain of 0.1 inches per hour might fill a 1000-gallon tank.
There are various means for storing water, but a preferred method for residential water storage is the use of a polyethylene tank. All polyethylene tanks are made from virgin polyethylene has been approved by the United States Food & Drug Administration for use with drinking water. They are also durable, relatively inexpensive, and available in a wide variety of colors. These properties make them an ideal choice for many residential users.
Proper use of a water storage tank includes addressing the problem of algae growth, which is a common problem associated with standing water. If left unchecked, algae growth may make the stored water unsuitable for its intended purpose. Thus, there is a need to prevent algae growth within water storage tanks. The growth rate of algae can be inhibited by limiting the water's exposure to ultraviolet radiation. Because most water storage tanks are placed outdoors, this generally means being exposed to sunlight.
The ability of a polyethylene tank to block ultraviolet radiation is dependent on the color of the tank. The darker the color of the tank, the more ultraviolet radiation that is blocked. Therefore, a black polyethylene tank would provide the best ultraviolet radiation protection and best inhibit the growth of algae. However, for a variety of reasons, a user might find that a black water storage tank is unacceptable. In some cases, a home owner's association limits the color of storage tanks. In some situations, the user just insists on having a non-black storage tank. Regardless of the reason, using a single-layer non-black polyethylene storage tank will result in accelerated algae growth. Thus, there is a need to provide water tanks of a variety of colors that still inhibit the growth of algae. By providing a polyethylene tank with a black inner layer and a non-black outer layer, a user can select a water storage tank color and still obtain improved algae inhibiting properties.